change rear ratio

MII

MII

Junior Member
my 49 F1 is 3:92.1, and I'm thinking of changing to 3:08.1
the transmission is heavy duty 3 speed on the floor
has any one done that and with good results?
it is an 8BA built by Walt
 
Depends on what your objectives are for the truck. Trucks are typically geared lower than a car. To me that would be a very high gear, is it going to be mostly a highway vehicle?
 
I have a '48 F=1 with the same gear ratio. I run 235/75 tires on the rear with no undue strain on the engine. I have run interstate highways to Charlotte motor speedway!
 

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Expect to stay in the box,(Aphrase used by truckers who constantly have to shift up and down) I tried it here in flat land oklahoma and it resulted in rotten fuel milege and a lot of shifting, mine was a 3:25. you my get better results , the rear diff is still on the shelf collecting dust. I had to run about 65 + mph to keep her from lugging down, also hard on the engine being in a hard pull at lower speeds. Lots of luck!
 
I forgot to say, my fuel mileage is 16-18 depending on how hard I drive it. Also, performance is very good. The engine is 276 ci.
 
thanks estout81 and Fordestes now I am totally confused, I have a 239 over .060
my rpm will b 2000 at 55 mph, I am looking at Speedway for the parts, is that the right place?
 
Like estout81 I compensated for a 4.11 rear in my '35 by going with a bigger diameter tires on rear, also wen with radials (love them). If your not concerned with a stock look it works well ( & looks cool ). Mine had 600 16's which I believe were approx 26" went to 235X85-16 approx 30 3/8" & believe reduced the 4.11 by 17% or approx to equivelent 3.50 rear. Runs great at highway speeds now.engine doesn't scream like it did at 60 to 70, just purrs now:D
 
I am new at this, but I think carrier, gears, shims, I assume the bearings will interchange, but new seals the axles should fit they are 19 spline
 
MII said:
I am new at this, but I think carrier, gears, shims, I assume the bearings will interchange, but new seals the axles should fit they are 19 spline
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If you’re looking for some input on parts for your differential I’d recommend you contact Chuck at Chucks Trucks. https://www.chuckstrucksllc.com/ He sold me a set of new gears for the tonner and handed out a lot of free advice on how to remove and set them up.
 
If there is nothing wrong with your rear end other than the ratio, I'd think long and hard about changing the gears. Unless you have experience at rear axle work you best leave it to a professional. Pricey!
 
Stuff is available for the Dana 44 with the 19-spline axles. If it's a Dana 41, I don't know. They had a different carrier but it might work on the taller ring gears. It depends on the size of the bolt circle.
 
The later 9" Ford rear end from '58 up to '72 will fall right in on your springs. You can buy a good used pickup rear a lot cheaper than changing the gears in your existing rear end. I did this swap for a friend and even used the brakes from the '52 rear end on the 9" rear end.
 
In the 9" there are many different ratios. There's usually a tag on them if nobody removed it. With your tire size and 3 speed trans. I would think something in the 3.50 range would give you a good highway cruising speed.
 
I would look long and hard at replacing the trans with a t5 5 speed. With a 3.90 rear you will be in the rpm range in 5th on the freeways and 4th will be good up to about 50 mph. You will still have the option of playing with rear gears if you feel it is necessary. Am running 5 speeds behind a flathead and a nailhead. Just my 2 cents worth.
 
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